The present invention relates to a squeezable tubular container and a process for the production thereof. More specifically, it relates to a squeezable tubular container which is formed from a composition of polyethylene and an ethylene/.alpha.-olefin copolymer and which is sterilizable at a high temperature or is heat-sealable or ultrasonically sealable, and a process for the production thereof.
With an advance in the modification of materials for packaging containers, there have been and are proposed containers which have the property of withstanding against sterilization treatment at a high temperature for a relatively long period of time such as retort treatment containers. Of these containers, there is actually used a container formed from a raw material prepared by laminating a polyolefin layer of polypropylene or high-density polyethylene on each surface of an oxygen-barrier resin layer, which is an intermediate layer and is formed of a thermoplastic resin such as highly heat-resistant polypropylene or high-density polyethylene; a saponification product of an ethylene-vinyl acetate copolymer; or nylon.
Since, however, the above raw material has a high elastic modulus, it cannot be necessarily said that such a raw material is suitable for a squeezable tubular container required to have flexibility. Low-density polyethylene has excellent flexibility but has a high shrinkage factor, and the defect is that it shrinks when subjected to high-temperature sterilization treatment. Low-density polyethylene is therefore not suitable as a raw material for a squeezable tubular container which is to be retort-sterilized.
On the other hand, it is well known that polyolefins typified by polyethylene undergoes a crosslinking reaction by radiation such as electron beam to improve heat resistance, chemical resistance and mechanical strength. For example, such polyolefins are practically used in cables and heat-shrinkable films. The improvement in the heat resistance, etc., is attributed to a three-dimensional net structure of molecules caused by the crosslinking. Since, however, three-dimensionally structured polyethylene is generally not melted even at a temperature higher than its melting point, it is poor in fusibility when fused by means of heat sealing or ultrasonic sealing, and the sealed portion is liable to peel with time or at the time of high-temperature sterilization treatment. Therefore, the polyethylene is not proper as a raw material for containers such as a squeezable tubular container required to tightly close a content therein by fusion such as heat sealing or ultrasonic sealing.